This invention relates to a monitoring method for use in a dry etching method of etching a silicon layer, so as to monitor status of the silicon layer.
A dry etching method of the type described is for use in etching a layer by the use of plasma resulting from a glow discharge in a gas filled in a hollow space. More specifically, such etching operation is advanced by virtue of various kinds of species activated in the plasma.
The dry etching method becomes indispensable for manufacturing a wide variety of semiconductor circuits, with development of a semiconductor integration technique. On manufacturing the semiconductor circuits, a silicon layer of, for example, polycrystalline silicon should often be etched as the layer by a dry etching method. It is very important to etch such a silicon layer on large scale integration or very large scale integration of MOS transistors, each having a gate electrode of polycrystalline silicon.
A conventional dry etching method uses a fluorine including gas in order to etch the silicon layer. With this method, isotropic etching is progressive and results in degradation of a precision of the etching. In addition, an etch rate is prone to be variable due to fluctuation of an electric field produced in the hollow space and the like.
In order to make anisotropic etching progress, another dry etching method makes use of a chlorine including gas. Such anistropic etching enables an improvement of the precision of etching. However, the etching rate is variable with this method also. It is therefore necessary to monitor the status of the silicon layer and to precisely detect the end of the etching. Otherwise, undercuts and the like inevitably takes place in the silicon layer. This is because a concentration of the activated species is rapidly increased after completion of the etching.
In a conventional monitoring method, a spectrum analysis is used to detect the end of the etching. The conventional monitoring method monitors emission spectra resulting from Si-radical and SiCl-radical. Such emission spectra are however susceptible to disturbance by any other emission spectra resulting from the remaining species.
For example, the Si-radical has spectrum components at 288.1 nm and 252.8 nm while the SiCl-radical has a spectrum component at 245 nm. On the other hand, carbon tetrachloride which is used as the chlorine including gas has emission spectra superposed on all of the above-mentioned spectrum components.